Post-operative arrhythmias occur commonly following pediatric cardiac surgery and can result in significant hemodynamic deterioration. Arrhythmias are more likely in the immediate post-operative period due to myocardial injury and ischemia, high catecholamine levels and electrolyte disturbances. At the same time, these arrhythmias are more likely to cause hemodynamic compromise due to the relatively tenuous cardiovascular function of patients immediately after cardiac surgery. Treatment of tachyarrhythmias often requires addressing two separate goals: termination of the arrhythmia and prevention of recurrences. These two objectives necessitate different treatment strategies in reentrant arrhythmias such as orthodromic reciprocating tachycardia, atrial fibrillation and intra-atrial reentrant tachycardia, including atrial flutter. Termination usually involves vagal maneuvers, adenosine administration, rapid pacing, or direct-current cardioversion. Prevention of recurrences, on the other hand, may require antiarrhythmic medications, although removal of central venous lines in the heart should be considered. Conversely, for automatic tachyarrhythmias, such as junctional ectopic tachycardia and ectopic atrial tachycardia, termination and prevention of recurrences usually involve similar modalities, including cooling, antiarrhythmic medications and correction of electrolyte abnormalities. Bradyarrhythmias, either sinus node dysfunction or AV block, can be treated by pacing with temporary epicardial wires in the short-term. In patients with persistent AV block for 7 days, however, permanent pacemaker placement may be required.